1. Field of the Invention
The present invention relates to a steel sheet coated with graphene and a method for manufacturing the same.
2. Discussion of Related Art
To provide a galvanized steel sheet, a zinc alloy-coated steel sheet, an aluminized steel sheet, an aluminum alloy-coated steel sheet, a cold-rolled steel sheet, and a hot-rolled steel sheet, which are used for automobile materials, household appliances, building materials, and the like, with corrosion resistance and plating adhesion, a surface treatment method of coating a chromate coating film has been generally performed. However, as various solutions to working environment and drainage disposal are required due to toxicity of hexavalent chromium, a chromium-free surface-treated steel sheet, which satisfies the characteristic requirements including corrosion resistance, alkali resistance, and conductivity without including hexavalent chromium, has been developed.
However, a surface-treated steel sheet manufactured using a conventional method such as organic or organic/inorganic composite coating should be exposed at a high temperature of 200° C. to 250° C. for a long period of time when it is used for interior/exterior materials of PDP panels. In this case, a change in color and a decrease in physical properties due to deterioration of resin components may be caused with a decrease in thermal stability of an organic material as a coating component.
To solve the problems of the surface-treated steel sheet, a plated steel sheet formed of a silicone-based or fluorine-based resin having excellent heat resistance has been used in the prior art. However, the plated steel sheet which is coated on an underlying layer having a thickness of approximately 5 μm to have a thickness of 20 μm to 30 μm has been widely used to ensure durability, which leads to difficulty in ensuring electric conductivity and an increase in manufacturing cost. For this reason, the plated steel sheet has been restrictedly used for interior/exterior materials to decorate the household appliances. In general, an anti-fingerprint steel sheet having a coating thickness of approximately 1 μm to 2 μm formed on a galvanized steel sheet has been widely used as a surface-treated steel sheet used for interior/exterior materials to decorate the household appliances.
Meanwhile, graphene has come into spotlight as a material whose thermal conductivity is at least 50% more excellent than that of carbon nanotubes. Graphene is a very thin material which has a two-dimensional planar structure in which hexagonal ring structures formed of carbon atoms are arranged periodically and has a thickness corresponding to one carbon atom. Graphene has remarkably excellent thermal stability, and also has thermal conductivity twice higher than diamond, strength 200 times higher than steel, and electrical conductivity in which an electric current 100 times higher than copper may be allowed to flow 50 times faster than silicon. The graphene has come into spotlight as a new next-generation material to replace silicon (Si) due to such excellent characteristics.
Since such graphene has characteristics such as thermal/chemical stability and lubricity, it may substitute a surface treatment solution of a galvanized steel sheet. Therefore, the graphene is probably applicable to the steel industry. More particularly, since electrons in the graphene behave like particles having no rest mass, they move remarkably faster than electrons in a conventional conductor or semiconductor. Since the graphene has significantly high current carrying capacity, it may also be developed as a material having excellent electrical conductivity by coating a metal substrate with graphene. In addition, since the graphene shows higher thermal conductivity than diamond and carbon nanotubes, it may be used as a metallic heat transfer material.
To apply graphene to the steel industry, it is required to grow graphene on a surface of iron which is the most important metal in the steel industry. Up to now, however, there is almost no report concerning a method for growing graphene on a surface of iron.
In the present invention, research on a method for growing graphene on a surface of iron has been conducted. As a result, the present inventor has found a graphene-coated steel sheet and a method for manufacturing the same.